For the small Red X by the lower corner of an icon, objects of your model that have the Generate checkbox disabled in their Properties dialogs are displayed in the Model Explorer with this Red X (shows small Red X by icon corner). To go to that topic in the Help file, go to the Search Tab | type: ‘Model Explorer’ | click ‘List Topics’ | and double-click ‘Model Explorer’.
For other type of icons (e.g. blue question marks), they are related to model verification and they mark verification hints, warnings and errors. To go to that topic in the Help file, go to the Search Tab | type: ‘Verify Model’ | click ‘List Topics’ | and double-click ‘Model Verification’.
